1. Field of the Invention
The present invention relates to a power supply apparatus using a half-bridge circuit, and more particularly to a power supply apparatus using a half-bridge type driving circuit, which is intended for the purpose of the compensation of a power factor, the achievement of a low crest factor and the maintenance of a constant output by being applied to a ballast or an inverter.
2. Background of the Related Art
Generally, an electronic ballast or an inverter used in a lamp converts a commercial power frequency into a high frequency and serves as controlling current so as to prevent over-current from flowing. The ballast may use various types of power factor compensation circuits in order to reduce current consumption, extend life span, and improve product reliability.
For example, a diode power factor compensation circuit may be used to vary a frequency as a method for accomplishing a high power factor and a low crest factor.
Although this method can achieve a high power factor and a low crest factor at low cost without using a dedicated integrated circuit (IC) of high cost for power factor compensation, there are problems due to a wide frequency variable range.
Specifically, if a frequency is raised, the efficiency of a resonance circuit deteriorates and thus the efficiency of the ballast is lowered. A wide frequency bandwidth increases an electro-magnetic interference (EMI) noise. In addition, a high frequency causes an increase in a power loss of a switching device and an increase in energy supplied to a filament, thereby shortening the life of a lamp tube and lowering the efficiency of the ballast.
If it is desired to control an output by varying only a frequency, since an output control dynamic characteristic is low, it is very difficult to set a feedback circuit for control. Moreover, since the overall characteristics of the ballast are poor, it is difficult to actually use the diode power factor compensation circuit.
Especially, when an input voltage is varied, since there are wide variations in power consumption, a crest factor, filament power, etc., a big difference occurs between a target characteristic value and an actual value.
Meanwhile, the use of the dedicated IC for power factor compensation, instead of the diode power factor compensation circuit, leads to an economic burden of cost, and an increase in the number of components and in size.